Bangarang February 2014 Backgrounder1

Plummet nets

(An Annotated Bibliography)

Eric Keen

Contents

Introduction

The Heron-Bangarang Sampler Design documentation

Literature Cited

Annotated Bibliography

                                                                                                               1 Bangarang Backgrounders are imperfect but rigorous reviews – written in haste, not peer-reviewed – in an effort to organize and memorize the key information for every aspect of the project. They will be updated regularly as new learnin’ is incorporated.

Introduction Plummet nets are a down-fishing zooplankton sampler that has no mouth obstructions and is cinched shut when the desired depth is reached. The design was first described in detail by Heron (1982), but used in published studies for a couple years prior. See the Annotated Bibliography for all published plummet net studies that this author can find. Plummet nets have been used for neritic and oceanic studies of copepods (Bradford 1977), euphausiids (Bartle 1976, Daly and Macaulay 1988, Hovekamp 1989, Daly 1990), and diverse assemblages (Newell & Bulleid 1975, Hopkins et al. 1993) for both biomass and behavioral research (Pierson et al. 2009). Because euphausiids actively avoid nets when warned of their approach by tow limes and bridles, and because their escape responses may have a predominant upward component (Daly and Macaulay 1988), they are effectively captured by plummet nets. Because the plummet net falls vertically quickly and begins sampling immediately once it hits the water, the problem of drift in strong currents is minimized; the boat may drift in relation to the net, but the net remains relatively stationary with respect to oceanography. Double-checking flowmeter readings by measuring the messenger rope as it is retrieved helps to constraint sample volume estimates. The simplicity and ease of this design is invaluable to small, man-powered sampling designs. However, as a plummet net, its samples are vertically integrated and possibly vulnerable to the lateral patchiness of zooplankters, some taxa more than others. In plummet nets, weight is another critical element of design that must be chosen carefully. The net’s total drag (a function primarily of mouth diameter) and the mouth ring’s weight will determine fall rate, which needs to remain between 1 m/s and 1.5 m/s in order to catch euphausiids. Larger nets require heavier rings; Heron’s (1982) plummet net is a WP2, 0.57m diameter, and needed to weigh 24kg in order to fall at 1.5 m/s; “anything heavier is difficult for one person to operate.” Published fall rates range from .7 m/s (Hovekamp 1989) to 1 m/s (Daly & Macaulay 1988; Daly 1990) to 1.5 m/s (Heron 1982). The appropriate weight can be determined using the trial methods outlined in Heron (1982). Because the net can be weighted such that it samples at a constant desired rate, there is no need for expensive speed-controlled winches.

First published design, Heron (1982)

The Heron-Bangarang Sampler

To design for the Bangarang Project’s goals within our constraints, we planned for daytime vertical tows with a plummet net (after Bartle 1976, Bradford 1977, Heron 1982, Daly & Macauley 1988 and Hovekamp 1989, among others). The elements we are contributing to Heron’s (1982) original published design are as follows.

1. The choke line connects to the tow line at both ends, providing a quicker and more reliable “dual-action” choking motion.

2. A fixed-length line runs from the ring to the shackle that joins the choke line to the tow line. This line serves as both a safety and as a limit to how tightly the Dacron can be choked, increasing the longevity of the net material.

3. A new cod-end design that allows the net to be dangled and prepare alongside the research platform before a drop.

4. Strength-bearing webbing running the length of the net, so that net can be suspended by the cod-end during preparation and sample preservation.

5. A mouth ring with spare eyebolts welded vertically at each quadrant, for mounting the flowmeter, adding weight and/or using the net with a bridle as an oblique sampler if needed.

The net itself was custom-manufactured by Aquatic Systems Designs for this project. The cylindrical portion of the net is non-porous black Dacron cloth, 70cm long. An elliptical band of webbing with nine equally spaced stainless steel caribeners runs from the mouth of one side of the Dacron to its opposite cone-ward side; these caribeners act as leads for the net’s choke lines. The conical section is 333 micrometer Nitex, 280cm long, for a total net length of 3.5m (Fig. 9). 3 bands of strength-bearing webbing run the length of the net and extend beyond the 3.5” diameter cod-end by 18”. These webbing bands terminate in 1” diameter stainless D-rings, which are held collectively by a large stainless caribener. The net is suspended by this caribener when being staged for a drop The 70cm-diameter mouth ring (area= 0.38 m2), made of solid ¾” 316 stainless steel, was manufactured at the SIO machine shop with 1/2” eye rings welded (with perpendicular orientation to ring, for hydrodynamics) at each quadrant of the ring, such that a bridle can be readily attached and used as a classic WP-2 oblique-tow net if needed. The ring weighs approximately 30 lbs. Retrieving the net manually is therefore difficult, especially when a moderate wind opposes a strong current. In 2013 all three researchers on board had to take turns pulling up the line. In 2014, a motorized line hauler will be added to the Bangarang. The porosity of our 333-micrometer mesh is 66% (according to the Dynamic Aqua website). Assuming a 100% sampling efficiency (which is a conservative estimate for a cyl-cone net, Tranter and Smith 1968), and given that a typical effective drop depth is 200m (seafloor depth permitting), the Heron-Bangarang net’s median sample volume in 2013 was calculated to be about 70 m3. Unfortunately, in 2013 Eric broke the calibrated flowmeter graciously loaned by the Scripps Pelagic Invertebrate Collection while trying to protect it in a hard-foam Pelican Case. When the case was clamped shut, the device was crushed. For 2014, two flowmeters will be calibrated, safely packaged and used in the field. These two meters will also be used to test filtration efficiency in situ.

The cinching of the net upon retrieval should halt flowmeter spin. Sample volumes calculated from the flowmeter can be checked against expected values given messenger rope payout and drop duration. To prevent clogging, a net designed for this tow duration in green waters must have an Open Area Ratio (OAR) of 5.4:1 or greater. Our net design has an OAR of approx. 6.5:1. Clogging was not observed in any 2013 tow. See the “Designing Nets” Backgrounder for more information. As the net descends, zooplankton are coalesced into the 3.5” OD two-piece cod-end bucket loaned from and designed by the SIO PIC. The two pieces are connected by quick-release butterfly shackles. 1”-diameter drainage holes with 333-micron mesh are drilled into its sides. For added security, the removable end is attached with a caribener to a thin line streaming from the net’s webbing tails. This line also prevented the choke line from cinching entirely, keeping strain on the Dacron and mesh to a minimum. In 2013 a back-up net was also kept on board (333 micron, 0.7m diameter, 9:1 open-area ration, loaned from SIO PIC). A concerted effort was made to record the GPS speed of the vessel to correct for the effect of lateral drift in fall rate calculations. Fall rates were observed in two ways: 1) by measuring the time elapsed between the submersion of two marks (typically 25 or 50 m apart) on the line as it was paid out, and 2) noting the total time and length of line paid out for the cast (Fig. 10). For the 2013 feasibility study, observed fall speeds indicate that Eric did a poor job of properly weighting the net. On average, the net free-fell at 0.785 ± 0.206 m/s (n=25, CV=26.18%), which is very close to the recommended speed for vertical tows outlined by UNESCO Working Party No. 2 (0.75 m/s, Tranter & Smith 1968) but half the recommended fall rate for capturing euphausiids (Heron 1982). This almost certainly contributed to our poor capture rate of adult krill. Before the 2014 season arrives, the net will be weighted and tested such that a fall rate of 1.25 – 1.5 m/s is consistently achieved. Our observations also suggested that fall rate vary slightly between less saline shallow (<75m) and deeper, more saline sections of the water column (down to 250m); mean fall rates calculated from shallow-water observations (mean=.844 ± 156 m/s, CV= 18.53%) differ significantly (Student’s t-test, df=37.177,p=.035) from those calculated for the deeper section (measured from the ~75m time mark to the end of the pay out (mean=.702 ± 0.286 m/s, CV=40.8%).

Figure 10. Fall rate of the Bangarang Heron net based on 50 time-depth observations from 25 drops. The lower left cluster of data was recorded using marks on the line as the net fell; the upper right cluster represents the end depth and duration of the tows. When possible, the lateral GPS speed of the drifting vessel was recorded as the net freefell; those data were used to correct the depth readings used in vertical fall rate calculations.

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Design Documentation Sent to Aquatic Systems Designs    

Plummet  net  design  for  Eric  Keen  Eric  Keen  

Student,  Scripps  Institution  of  Oceanography  ericmkeen@gmail.com  

707-­‐238-­‐2232    28”  (70cm)  diameter  cylindrical-­‐conical  net  Total  length:  350cm    Cylindrical  section:  Length:  70cm  Truly  cylindrical;  the  mouth  does  not  reduce  at  all.  Material:  Dacron  sail  cloth  (dark  blue/green  color  if  possible)    Conical  section:  Length:  280cm  Material:  Nitex  mesh  (dark  blue/green  color  if  possible)  Mesh  size:  300  –  333  micrometer    Cod  end  diameter:  3.5”  or  9cm    *No  bucket  or  ring  wanted.  Modified  net  only.    Features:  Mouth  grommets:  10  –  12  grommets  encircling  the  mouth,  for  being  bound  to  the  net  ring.    Webbing  lines:  3  strong  webbing  lines,  evenly  spaced  around  net,  that  run  the  length  of  the  net  AND  BEYOND  the  cod  end  for  18  inches.    Each  of  these  webbing  lines  end  in  a  weight-­‐bearing  sewn  loop  around  a  1”  stainless  ring.  Webbing  reinforcement  may  be  added  elsewhere  on  the  net  as  deemed  necessary  for  high  strength  (the  net  ring  will  be  heavy).    A  choke  loop:  An  ellipse  of  webbing  on  the  cylindrical  Dacron  sail  cloth.  One  end  meets  the  base  of  the  net  mouth  and  the  other  end  touches  the  boundary  of  the  net  mesh.  The  webbing  has  sewn  in  eight  1”  rings  distributed  evenly  around  it.    Be  particularly  careful  that  one  ring  is  located  at  the  point  closest  to  the  net  mouth  and  another  is  directly  opposite  the  ring,  at  the  choke  loop’s  highest  point  near  the  boundary  of  the  Dacron  and  the  mesh.    [FYI:  Rationale]  This  is  a  vertical  net  that  samples  as  it  descends.    The  choke  line  will  be  loose  when  the  net  is  released  at  the  surfaced,  and  will  fall  freely  along  with  the  net.  When  the  desired  depth  is  reached,  the  choke  line  will  become  taught  and  strangle  the  net  through  the  angled  ellipse  of  rings  on  the  Dacron  cloth.  The  net  will  dangle  with  the  mouth  vertical  and  the  net  limp,  and  it  will  be  hoisted  by  the  choke  line.  While  the  choke  line  is  being  prepared  for  the  next  tow  back  at  the  surface,  the  net  will  be  suspended  from  a  davit  by  the  3  webbing  lines  extending  beyond  the  cod  end.        

   

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Literature Cited Bartle, J.A. 1976. Euphausiids of Cook Straight: a transitional fauna? N.Z. J. Marine Freshwater Resources

10:559-576.

Bradford, J.M. 1977. Distribution of the pelagic copepod Temora turbinate in N.Z. coastal waters, and possible trans-Tasman population continuity. N.Z. J. Mar. Freshwater Res. 11:131-144.

Bradford, J.M. and P.E. Roberts. 1978. Distribution of reactive phosphorus and plankton in relation to upwelling and surface circulation around New Zealand. N.Z. J. Mar. Freshwater Res. 12:1-15.

Clutter, R.I., and M. Anraku. 1968. Avoidance of samplers. Monogr. Oceanog. Methodol. 2:57-76. UNESCO.

Daly, K.L. 1990. Overwintering development, growth, and feeing of laral Euphausia superba in the Antarctic marginal ice zone. Limnol. Oceanogr. 35(7):1564-1576.

Daly, KL and Mc Macaulay. 1988. Abundance and distribution of krill in the ice edge zone of the Weddell Sea, austral springs 1983. Deep-Sea Research 35(1):21-41.

Heron, A.C. 1982. A vertical free fall plankton net with no mouth obstructions. Limnology and Oceanography 27(3):380-383.

Hopkins, T. L., T.M. Lancraft, J.J. Torres, and J. Donnelly. 1993. Community structure and trophic ecology of zooplankton in the Scotia Sea marginal ice zone in winter (1988). Deep-Sea Research I(4):81-105.

Hovekamp, S. 1989. Avoidance of nets by Euphausia pacifica in Dabob Bay. Journal of Plankton Research 11(5):907-924.

Newell, B.S., and N.C. Bulleid. 1975. A schema of the nitrogen cycle off Port Hacking, New South Wales. Aus. J. Mar. Freswhater Res. 26:375-388.

Pierson, J.J., B.W. Frost, D. Thoreson, A. W. Leising, J.R. Postel, M. Nuwer. 2009. Trapping migrating zooplankton. Limnology and Oceanography: Methods 7:334-346.

Annotated Bibliography Published studies that have used plummet nets (Chronological order). Bartle, JA. 1976. Euphausiids of Cook Strait: a transitional fauna? New Zealand Journal of Marine and Freshwater Research, 10(4):559-576. - Samples were taken day and night. - Monthly samples were used to describe seasonal variation. “Nearly all samples were collected using a free-fall cylinder-cone net with a mouth diameter of 57 cm (mouth area 0.25 m2) and amultifilament nylon mesh of 0.57mm aperture. The basic design of the free-fall net was developed by A.C. Heron (Division of Fisheries and Oceanography, CSIRO, pers. comm., 1968) and has not yet been published, but that used in this survey was a modified version and a detailed account of its design and performance can be found in Bartle (unpublished 1972). The greatest advantage of the free-fall net was the absence of obstructions in front of the mouth: extensive avoidance would occur if a long towing line and bridges had warned euphausiids of the net’s approach. A free-fall net sinks because of the weight of its heavy steel ring (36 kg in this case) and captures plankton as it falls. When it reaches a prearranged depth the net is throttled and hauled up. Vertical samples were made from the surface to depths of 36m (20 fathoms), 91.5m (50 fathoms), and 183m (100 fathoms) at most stations. As no opening-closing apparatus was available, subtractive analyses of successively deeper samples were made, and the composition of the deeper plankton was determines after elimination of material found in shallower samples. Subsampling was often necessary, as up to 5000 euphausiids could be found in a single sample.” Bradford, J.M. 1977. Distribution of the pelagic copepod temora turbinata in New Zealand coastal waters, and possible trans-tasman population continuity. New Zealand Journal of Marine and Freshwater Research 11(1):131-144. “The zooplankton samples were taken with a “WP2” net (Fraser 1966, 1968) of 0.2mm monyl nylon mesh, 0.57m mouth diameter, modified for “free-falling” as suggested by A.C. Heron and D.J. Tranter (CSIRO, Australia, pers. comm.). In this method, the mouth of the net was held open by a 20 kg galvanised iron hoop. The net was throttled at a pre-determined depth (a maximum of 200m or just above the sea bed) by a trailing rope. Stations were occupied at standard depths (25m, 50m, 100m, 200m) whenever possible, with additional stations over the continental slope. Samples were preserved immediately in 2% formaldehyde.” These samples are used again in: Bradford, J.M. and P.E. Roberts. 1978. Distribution of reactive phosphorus and plankton in relation to upwelling and surface circulation around New Zealand. N.Z. J. Mar. Freshwater Res. 12:1-15. Heron, A.C. 1982. A vertical free fall plankton net with no mouth obstructions. Limnology and Oceanography 27(3):380-383.

Notes: - Closed after a preselected time by a strangling rope secured aboard ship - Eliminates 3-point bridle and the long wire in front. - Depth and volume filtered are unaffected by drift. - “only requires a warping drum after closure”, no winch needed. - Vertical bridles cause escape responses (Clutter and Anraku 1968) - Standard vertical hauls also have specific winch requirements (speed, speed control, meter blocks). - Closing collar is a cylinder of Dacron sailcloth of the same diameter as the net mouth and slightly longer than the diameter of the net mouth. - Nonfiltering, so it doesn’t contaminate or cause loss of zooplankton when it is closed. - Series of small rings around color takes strangling rope. - Place the small rings by drawing up the strangling collar, marking the shortest circumference around the bunched material. These marks describe an arc with radius equal to the mouth diameter. - Ring can be lead-filled pipes bolted together. - Ring can be a streamlined steel band with low profile to the flow. - Ring weight is chosen according to the speed desired and the resistance of the net. - Desired speed is usually 10 cm/s approaching the mesh (which, for 6:1 OAR nets is a tow speed of 1.5 m/s – Tranter and Smith 1968) or less (which minimized filtration damage to plankton). - For a WP2 type net, a 24kg weight is needed to achieve this. Anything heavier is difficult for one person to operate. - How to know required weight: Attach weight to net with a 3-pt bridle until the net combination drops to the end of a measured rope at the desired speed – with no horizontal drift relative to vessel. - Air initially trapped in bucket does not affect operation. - Strangling rope is fixed to the ship at a length grater than the expected length of the drop. - When the time to reach the desired depth has elapsed, payout of the rope is stopped, thus closing the net. - Stopping according to timing has a precision of <1%, at least as good as simple depth-measuring instruments. - Compensation in timing could be introduced to increase accuracy when severe drift is expected. Mark the rope at 1-m intervals BEYOND the desired depth, then measure the rope angle after closure – this allows an easy approximation of the depth reached if no closing flowmeter or time-depth meter is available. - Flowmeter should be closable by action of strangling rope to avoid registering on the way up. - Clogging is unlikely to be a problem, but an extra flowmeter could be used to measure it. - When viewed underwater, upon closure, no zooplankton were ejected forward (which can happen in Nansen systems!) - Net is then recovered by warping the rope around a drum or leading it through a line hauler. - If a stuffing box is used, the weight of net will pay out the rope freely from the basket on the next drop. - Free-fall nets also work for phytoplankton. - If the ship drifts during a normal vertical haul, the net will traverse a grater distance than the depth, thus filtering a larger volume of water. - Because the plummet net falls quickly, vertically, and begins sampling immediately, the drift problem is minimized. - Free fall net has been used in Bartle 1976, Newell and Bulleid 1975, Bradford 1977, Bradford and Roberts 1978. - “Not only fulfilled the objectives of its design, but also is convenient to use.”

Daly, KL and Mc Macaulay. 1988. Abundance and distribution of krill in the ice edge zone of the Weddell Sea, austral springs 1983. Deep-Sea Research 35(1):21-41. This study investigated the effect of ice edge zone on the abundance and distribution of Antarctic krill using both acoustic and net sampling methods in the Weddell Sea. “Net sampling was restricted to vertical tows because of the difficulty of working in the pack ice. In an effort to minimize krill avoidance, a downward-fishing, closing vertical net was used. The “Plummet” net, a 1 m2 net with a 560 micrometer mesh, was deployed from the surface at 1 m/s to the desired depth, then closed with a messenger. Haul depth of the net tows, typically between 50 and 140m, was generally determined by the depth of the acoustic targets from echograms. Samples were preserved in buffered 4% formaldehyde.” “Only late larvae (furcilia 5 and 6) and juveniles [of Euphausia superba] were collected in net tows.” “Acoustic echograms indicate that no other net tows, except at Sta. 7, sampled swarms. Instead, they sampled a dispersed or “background” level of juvenile krill which averaged about 0.014 individuals per cubic meter. The higher krill biomass values at the eastern side of the survey area are due in part to swarms at Stas 5 and 7. Neverthelss, 81% of the net hauls on the eastern transect caught krill, while only 25% of those on the western transect caught krill. This is in contrast to acoustic estimates which showed an increase in biomass on the western transect.” “Downward-looking acoustics cannot detect krill close to the surface (<10 cm) nor concentrations below a minimum detection level (ca 0.2 g per cubic m)….Net estimates content with avoidance and gear selectivity problems, and very few data are collected for an expended amount of effort. However, nets can sample near the surface and for minimum concentrations of krill. In addition, net samples are necessary for species identification, life history and size-class information. Therefore, to obtain the most accurate picture of the abundance and distribution of krill, both net sampling and acoustics must be used.” Hovekamp, S. 1989. Avoidance of nets by Euphausia pacifica in Dabob Bay. Journal of Plankton Research 11(5):907-924. “Plummet nets with minimum turbulence and vibration in, and ahead of, the mouth are recommended for sampling euphausiids until better technology becomes available.” “There is a widely held conviction that euphausiids are more accurately sampled when the direction of net haul departs from vertically upward – the greater the departure, the less avoidance. The epitome is then plummet sampling, i.e. vertically downward hauls. Macaulay (197) posits that Euphausia pacifica, the predominant species in Puget Sound and much of the coastal Northeast Pacific (Brinton 1976), detects nets visually and the differential catch between up and down hauls is a result of a downward-oriented detection, an avoidance response of upward swimming, or some combination of these. An important consideration in up versus down catches is that plummet nets usually have little or no rigging in front of the net mouth whereas up hauls have the tow cable preceding in the path of the net.” “The purpose of the present experiment was to quantitatively assess the effects of haul direction and the presence or absence of daylight upon net avoidance by euphausiids. A variety of net hauls were conducted in a deep water (195m) bay of Puget Sound over an 18 month period. The euphausiid

community of this bay was dominated by E. pacifica. Less abundant by two orders of magnitude was Thysanoessa longipes. Occasionally, a roque Tessarabrachion oculatus turned up in a deep sample.” “Field sampling was conducted in Dabob Bay…Euphausiids were collected in vertical hauls with a 571 micrometer mesh plummet net with a 1m diameter mouth. The mouth of the net was fitted with a hose packed with 45 kg of lead shot so that the net could be fished downward as well as upward….” “Samples were collected on six cruises from August 1986 to February 1988. Plummet net hauls were made in triplicate with the exception of October 20, 1987, when they were duplicate…” “The plummet net was fish both upward and downward in sets of hauls as near to noon and midnight as the ship schedule would allow….For upward hauls the cod end was weighted and the net was lowered in the open position until the mouth was at 175m depth. After a 10 second pause it was hauled up. For downward hauls the net was suspected from the cod end with the mouth open downward. The net was then lowered until the mouth was at 175m depth where a previously released messenger tripped the net, releasing the cod end to fall beneath the mouth, which was now suspended sideways. In this posture the net was hauled to the surface….” “For both up and down hauls tow speed ranged between 0.7 and 0.8 m/s, depending on the power source. “[Results] Catch is different between day and night samples, generally being greater at night, although not in the summer cruises. Catches from down hauls are always greater than up hauls, on average about nine times greater.” “The effect of direction changes between day and night, with down hauls during the day catching on average about eight times as much as day-up hauls, while night-down hauls catch ~10.5 times as much as comparable ups. This interaction is significant (P=0.49), but considering the small magnitude of this effect, it seems that this difference is not biologically important. The effect of direction also changes between size classes. Down hauls catch approximately twice as many of the 30-9mm, six times the 9-15mm and 14 times the >15mm euphausiids relative to comparable up hauls.” “Daylight increases the catch on the summer cruises almost three-fold. On October 1 daylight makes little difference. Darkness increases average mean catch by factors of three and 12, respectively, in late October and February.” “The plummet net, fished downwards, clearly demonstrated enhanced catches versus upward tows.” “Visual detection of nets and subsequent avoidance (Macaulay 1977) by E. pacifica may indeed be taking place but there is no evidence to suggest that it is not relatively constant regardless of surface light level or direction of tow. Differential catches between haul types are consistent with movement away from the vibrational stimuli of the tow cable (Fleminger and Clutter 1965). “Comparison with acoustic data (Daly and Macaulay 1988) suggests that even the most careful net sampling seriously underestimates euphausiid abundance. Acoustic techniques appear to be very applicable to euphausiid distribution and abundance study (Macaulay 1977). But the necessity of ground-truthing acoustic data still leaves a need for accurate net sampling. The motility, behavior and scale of sensory acuity of euphausiids puts them beyond the scope of traditional plankton sampling. Much larger nets with more cryptic deployment techniques are called for. In the meantime, the best performance will be obtained from contemporary equipment if it is fished with no components in, or ahead of, the mouth of the net.”

Daly, K.L. 1990. Overwintering development, growth, and feeing of laral Euphausia superba in the Antarctic marginal ice zone. Limnol. Oceanogr. 35(7):1564-1576. “Euphausia superba was collected at discrete depths between 0-100, 100-200, 200-400, 400-600, and 600-1,000m during day and night. In heavy pack ice, net sampling was necessarily restricted to vertical tows (1 m/s) with two downward-fishing, closing 1-m2 plummet nets of 1.6mm and 163 micrometer mesh, respectively. Sampling continuity was preserved by also using these nets for open-water collections. In addition, larvae were collected with a small plankton net (0.5m diameter, 163 micrometer mesh) nested inside a 1.85 m2, closing Tucker trawl at the same depth intervals as the plummet nets. Oblique tows were made in open leads in the ice when possible and in open water. All samples were preserved in buffered 4% formaldehyde.” Hopkins, T. L., T.M. Lancraft, J.J. Torres, and J. Donnelly. 1993. Community structure and trophic ecology of zooplankton in the Scotia Sea marginal ice zone in winter (1988). Deep-Sea Research I(4):81-105. “Microzooplankton (<1 mm) was sampled with 30 l water bottles at the locations shows in Figure 1. Eleven casts were made with 30 l bottles (137 samples) collecting at the surface, 10, 25, 50, 75, 100, 150, 200, 300, 400, 600, 800, and 1000m horizons. Occasional samples were taken at depths of 500, 700 and 900m. Sample water was passed through 30 micrometer gauze for quantitative sampling of metazoan microzooplankton (<1 mm). “Meso-macrozooplankton (1-20mm) were collected in vertical series with 1 m2, 162 micrometer mesh opening-closing plummet nets. Standard sampling zones (A-E) were 0-100, 100-200, 200-400, 400-600, and 600-1000m. Nineteen vertical series were attempted yielding 105 collections. Oblique tows also were made with a collapsible 0.75m2, 162 micrometer mesh net mounted in the mouth of an opening-closing Tucker trawl. These collections provided supplementary material for diet analysis and information on the distributions of relatively uncommon species. Fifty-four oblique samples were obtained in various depth zones from the surface to 1000m.” Pierson, J.J., B.W. Frost, D. Thoreson, A. W. Leising, J.R. Postel, M. Nuwer. 2009. Trapping migrating zooplankton. Limnology and Oceanography: Methods 7:334-346. In this paper, a plummet net design (among other designs) was adapted to capture zooplankton as they migrated vertically. The net would be lowered closed to the desired depth, opened, left open and stationary for a determined length of time, then closed and hauled in.